56 
STRANGE DWELLINGS . 
generally have a bed of muddy matter between their shells and 
the walls of their dwelling, the Helix saxicava keeps his tunnel 
perfectly clean and neat. 
4 5th. When the liquor alluded to as forming a fatty aureole 
round the tunnel penetrates into pre-existing clefts in the rock, 
’t provokes the growth of a microscopic lichen, which also grows 
in the tunnels in places after the liquor has evaporated. 
4 6th. The tunnels of the Helix saxicava are always irregular, 
bearing no relation to the size or shape of the excavators, 
whereas, in other excavating molluscs, the shape of the hole 
always bears some relation to its occupant, and also the excava- 
tions are alike for all animals of the same species/ 
There is an opinion that the gastric juice secreted in the 
stomach may be the means through which the tunnelling is con- 
ducted, and that instead of being employed as food within the 
body it is poured out upon the stone, so as to dissolve it, the 
softened substance being then removed by the foot. The Boring 
Snails do not congregate together during hibernation, as is the 
well-known custom of the garden species, but are always solitary. 
Sometimes two or even three are found in the same burrow, but 
then they are always at some distance from each other, and form 
supplementary tunnels of their own. In my own specimen there 
is a curious example of this peculiarity, where the snail has con- 
trived to bore completely through the barrier that separates it 
from a neighbouring tunnel, and has made a hole as large as the 
keyhole of an ordinary writing-desk, and nearly of the same 
shape. 
There are many marine boring molluscs, some of which exca- 
vate mud, others stone, and others timber. Of the mud-borers 
I have little to say, few of them possessing points worthy of 
notice. Perhaps the most noteworthy of these is the common 
Gaper Suell ( Mya arenarid), so called, because one end of the 
shell gapes widely, in order to permit the passage of a long and 
stout tube. In a specimen now before me, the tube is between 
three and four inches in length, and at the base is large enough 
to admit the thumb. As, however, it gradually tapers to the 
